The homopolymerization of 2,3‐dimethyl‐1,3‐butadiene and the copolymerization of 1,3‐butadiene/2,3‐dimethyl‐1,3‐butadiene using the catalyst system AlEt₂Cl‐Co(acac)₂. A structural investigation of the products

Abstract

The homopolymerization of 2,3-dimethyl-l,3-butadiene with the catalyst system AlE%Cl-Co(acach affords polymers consisting of about 81 % cis-l,4-units and 19% 1,2-units.The copolymerization of 1,3-butadiene/2,3-dimethyl-l,3-butadiene using the same system is of the ideal type and the composition of the copolymers is practically identical with that of the monomer mixture. The structure of the copolymers depends on their composition. The butadiene units, which are more than 95% cis-1,4 in the homopolymer, become partially 1,2 in the copolymers; their amount increases with increasing dimethylbutadiene content. Conversely, the fraction of dimethylbutadiene units with 1 ,Zstructure decreases in the copolymers with increasing butadiene content. In the copolymers containing more than 50% of butadiene, the dimethylbutadiene units are practically all cis-l,4. The analysis of sequence distribution shows that the 1,2-butadiene units in the copolymers are not randomly distributed but are mostly adjacent to dimethylbutadiene units. The results obtained with dimethylbutadiene are compared with those reported for the homopolymerization of isoprene and the copolymerization of isoprene/ butadiene using the same catalyst system.

Polymerization of butadiene using neodymium versatate-based catalyst systems: preformed catalysts with SiCl4 as halide source

“…Binary and ternary catalytic systems based on neodymium salts represent an important class of diene catalysts and offer a number of advantages over conventional transition metal systems 1–5. In particular, interest has focused on their ability to generate polydienes of high cis ‐1,4 stereospecificity with good abrasion and fatigue resistance, which in tyre manufacture has significant appeal 4…”

The Influence of Back-Biting Interaction on the Polymerization of Conjugated Dienes in the Presence of Ziegler−Natta Catalysts

“…In the presence of different catalysts, the back-biting could be retained upon coordination of the monomer (see, for instance, Tobisch et al and references therein), and then it could play a more important role in determining the product of the polymerization reactions. That could be the case of Co(acac) 2 −H 2 −AlEt 2 Cl, − whose puzzling behavior has been cited before. In fact, the findings that the amount of 1,4 units increases with increasing amount of butadiene and that, in the butadiene and 2,3-dimethyl-butadiene copolymerization, the 1,2 butenylic units are always preceded by the 2,3-dimethyl-butenylic are evidence of the effect of the back-biting interaction in determining the reactivity of the last repeating unit.…”

“…There is substantial evidence that in the polymerization of conjugated dienes by Ziegler−Natta catalysts the growing polymer chain (P) plays a role both in determining the position of insertion of the incoming monomer (M) (1,2 vs 1,4 polymerization) and the energetics of the propagation reaction . An example is provided by isoprene and butadiene copolymerization in the presence of CpTiCl 3 −MAO (Cp = cyclopentadyenil, MAO = methyl aluminoxane), which copolymerize almost randomly, despite the large difference that the two monomers exhibit in homopolymerization experiments. − Such behavior can only be rationalized by assuming that the rate of the whole propagation reaction is determined to a larger extent by P rather than by M. − Besides, in the copolymerization of butadiene and isoprene in the presence of Co(acac) 2 −H 2 −AlEt 2 Cl (acac = acetylacetonate, Et = ethylate), the chemoselectivity appears to be strongly affected by the nature of the ending units of R. − In fact, Co(acac) 2 −H 2 −AlEt 2 Cl yields polybutadiene containing more than 99% of 1,4 units, whereas for polyisoprene 9 and poly-2,3-dimethyl-butadiene, the amount of 1,4 units is less than 70%. However, when butadiene is copolymerized with isoprene, the butadiene units become partly 1,2 in a proportion that increases with the content of isoprene, and correspondingly, the amount of cis 1,4 isoprene units increases with the butadiene content in the copolymer.…”

“…However, when butadiene is copolymerized with isoprene, the butadiene units become partly 1,2 in a proportion that increases with the content of isoprene, and correspondingly, the amount of cis 1,4 isoprene units increases with the butadiene content in the copolymer. Besides, in butadiene-2,3-dimethyl-butadiene copolymerizations, the 1,2 butadiene units are always preceded by 2,3-dimethyl-butadiene units …”

“…Besides, in butadiene-2,3-dimethyl-butadiene copolymerizations, the 1,2 butadiene units are always preceded by 2,3-dimethyl-butadiene units. 10 To better understand the role played by the growing polymer chain, we have studied, by means of ab initio calculations and orbital interaction diagrams, the active species for the homopolymerization and the copolymerization of butadiene and isoprene in the presence of CpTiCl 3 -MAO. Since it is possible that in the presence of many Ziegler-Natta based catalysts P folds on itself, forming a bonding interaction with the metal center (back-biting interaction), [11][12][13][14][15] we have modeled P by considering both of the two ending repeating units.…”